Alkaline electrochemical cell with a blended zinc powder

ABSTRACT

An electrochemical cell with a blended zinc powder is disclosed. The blended zinc powder includes selected portions of a first zinc powder and a second zinc powder. In a preferred embodiment, the first and second powders are divided into groups based on ranges in their particle size distribution. Particle characteristics such as roughness and elongation are used to selected groups of both powders that are combined to produce the blended zinc powder. The blended zinc powders enable battery manufacturers to maximize the cell&#39;s run time while minimizing the cost of the zinc.

BACKGROUND OF THE INVENTION

This invention generally relates to alkaline electrochemical cells. Moreparticularly, this invention is concerned with alkaline cells having ananode that contains blended zinc powder.

Cylindrically shaped electrochemical cells are suitable for use byconsumers in a wide variety of devices such as flashlights, radios andcameras. Batteries used in these devices typically employ a cylindricalmetal container to house two electrodes, a separator, a quantity ofelectrolyte and a closure assembly that includes a current collector.Typical electrode materials include manganese dioxide as the cathode andzinc as the anode. An aqueous solution of potassium hydroxide is acommon electrolyte. A separator, conventionally formed from one or morestrips of paper, is positioned between the electrodes. The electrolyteis readily absorbed by the separator and anode.

Commercially available cylindrical alkaline batteries use an anode thatincludes zinc in particulate form. The anode is a gel that has absorbedan aqueous electrolyte. The zinc particles are uniformly dispersedwithin the gel so that particle-to-particle contact establishes anelectrically conductive matrix throughout the anode. A current collectorcontacts the zinc and provides an electrically conductive path betweenthe anode and one of the cell's terminals.

Due to the ever present desire to provide consumers with betterperforming batteries, battery engineers are constantly striving toimprove the length of time that a battery will power a consumer'sdevice. At the same time, the need to reduce the cost of the cell, whilemaintaining the cell's service performance, has become paramount.Previous attempts to improve service have included modifications to thezinc's alloy, changes to the shape of the zinc particles, modificationsto the zinc powder's particle size distribution and forming free flowingzinc particles into agglomerates of zinc. For example, U.S. Pat. No.6,022,639 describes incorporating zinc flakes into zinc powder that isused in an alkaline electrochemical cell. Unfortunately, the use of zincflakes is known to substantially increase the viscosity of the gelledanode containing the zinc flake. The increase in viscosity can causeprocessing problems that adversely impact the efficiency of the cellmanufacturing process. U.S. Pat. No. 6,284,410 describes adding zincfines or zinc dust to a zinc powder. The addition of fines or dust isdescribed as beneficial to the cell's overall performance. However,adding the fines or dust is known to increase the viscosity of thegelled anode which can cause processing problems in the cellmanufacturing process. Numerous attempts have been made to improve thecell's run time by alloying one or more elements, such as bismuth,indium, aluminum, lead, tin, or manganese, with the zinc. Alloyingelements with zinc has proven effective at increasing the service of thecell but the alloying process incurs additional expense at the zincmanufacturing facility which ultimately increases the cost of the cell.Forming zinc agglomerates from free flowing zinc powder is described inU.S. published patent application 2004/0013940 A1. While agglomerates doimprove the cell's run time on certain service tests, the process stepsneeded to form the agglomerates also increases the cost of the zinc andthus the cost of the battery. All of the changes to the zinc describedabove can be collectively described as an industry wide effort toengineer the zinc powder to improve cell performance by altering certainphysical and/or chemical characteristics of the zinc powder. However,there continues to be a need for further advances in the development ofzinc powders that will enable service improvements while minimizing anyadditional cost to the cell or, alternatively, reducing the cost of thezinc while maintaining the cell's service.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an electrochemical cell with zinc powderthat is economical to manufacture and provides desirable run time whenused in a device.

In one embodiment, the electrochemical cell of the present inventionincludes a first electrode that is a blend of at least a first powderand a second powder. Both the first and second powders have particleswithin a common particle size range. The first powder's particles in thecommon particle size range have a roughness index value that is at least2.0 percent higher than the roughness index value of the second powder'sparticles in the common particle size range.

The present invention also relates to an electrochemical cell thatincludes a mixture of zinc powders. The mixture includes zinc particlesfrom a first powder and at least a second powder. The range of particlesizes in the first powder and the range of particle sizes in the secondpowder do not overlap.

The present invention also relates to an electrochemical cell thatincludes a mixture of zinc powders obtained by segregating a firstpowder into at least two groups based on particle size, segregating asecond powder into at least two groups based on particle size, whereinat least one group from the first powder and one group from the secondpowder have a common particle size range and the group in the firstpowder's common particle size range has an average roughness index valuethat is at least 2.0 percent higher than the average roughness indexvalue of the group in the second powder's common particle size range.Then blending the group from the first powder's common particle sizerange with at least one group from the second powder.

The present invention also relates to a process for producing a blendedzinc powder. The process includes the following steps. Segregating afirst powder into at least two groups based on particle size.Segregating a second powder into at least two groups based on particlesize. Blending at least one group from the first powder with at leastone group from the second powder thereby forming the blended zincpowder. At least one group from the first powder and one group from thesecond powder have a common particle size range. The particles in thefirst powder's common particle size range have an average roughnessindex value that is at least 2.0 percent higher than the averageroughness index value of the particles in the second powder's commonparticle size range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an electrochemical cell of thisinvention;

FIG. 2 is a graph of roughness index versus particle size ranges for twozinc powders;

FIG. 3 is a graph of elongation index versus particle size ranges fortwo zinc powders;

FIG. 4 is a graph of two particle size distributions;

FIG. 5 is a graph of a particle size distribution; and

FIG. 6 is a chart showing test results from three service tests.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more particularly to FIG. 1, there isshown a cross-sectional view of an assembled electrochemical cell ofthis invention. Beginning with the exterior of the cell, thecell'components are the container 10, first electrode 50 positionedadjacent the interior surface of container 10, separator 20 contactingthe interior surface 56 of first electrode 50, second electrode 60disposed within the cavity defined by separator 20 and closure assembly70 secured to container 10. Container 10 has an open end 12, a closedend 14 and a sidewall 16 therebetween. The closed end 14, sidewall 16and closure assembly 70 define a volume in which the cell's electrodesare housed.

First electrode 50 includes a mixture of manganese dioxide, graphite andan aqueous solution containing potassium hydroxide. The electrode isformed by disposing a quantity of the mixture containing manganesedioxide into the open ended container and then using a ram to mold themixture into a solid tubular shape that defines a cavity which isconcentric with the sidewall of the container. First electrode 50 has aledge 52 and an interior surface 56. Alternatively, the cathode may beformed by preforming a plurality of rings from the mixture comprisingmanganese dioxide and then inserting the rings into the container toform the tubularly shaped first electrode.

Second electrode 60 is a homogenous mixture of an aqueous alkalineelectrolyte, a blend of two or more zinc powders, and a gelling agentsuch as crosslinked polyacrylic acid. The aqueous alkaline electrolytecomprises an alkaline metal hydroxide such as potassium hydroxide,sodium hydroxide, or mixtures thereof. Potassium hydroxide is preferred.The gelling agent suitable for use in a cell of this invention can be acrosslinked polyacrylic acid, such as Carbopol 940®, which is availablefrom B. F. Goodrich, Performance Materials Division, Cleveland, Ohio,USA. Carboxymethyylcellulose, polyacrylamide and sodium polyacrylate areexamples of other gelling agents that are suitable for use in analkaline electrolyte solution. The blended zinc powder may be pure zincor an alloy comprising an appropriate amount of one or more of themetals selected from the group consisting of indium, lead, bismuth,lithium, calcium and aluminum. A suitable anode mixture contains 67weight percent zinc powder, 0.50 weight percent gelling agent and 32.5weight percent alkaline electrolyte having 40 weight percent potassiumhydroxide. The quantity of zinc can range from 63 percent by weight to70 percent by weight of the anode. Other components such as gassinginhibitors, organic or inorganic anticorrosive agents, binders orsurfactants may be optionally added to the ingredients listed above.Examples of gassing inhibitors or anticorrosive agents can includeindium salts (such as indium hydroxide), perfluoroalkyl ammonium salts,alkali metal sulfides, etc. Examples of surfactants can includepolyethylene oxide, polyethylene alkylethers, perfluoroalkyl compounds,and the like.

The second electrode may be manufactured by combining the ingredientsdescribed above into a ribbon blender or drum mixer and then working themixture into a wet slurry.

Electrolyte suitable for use in a cell of this invention is athirty-seven percent by weight aqueous solution of potassium hydroxide.The electrolyte may be incorporated into the cell by disposing aquantity of the fluid electrolyte into the cavity defined by the firstelectrode. The electrolyte may also be introduced into the cell byallowing the gelling medium to absorb an aqueous solution of potassiumhydroxide during the process used to manufacture the second electrode.The method used to incorporate electrolyte into the cell is not criticalprovided the electrolyte is in contact with the first electrode 50,second electrode 60 and separator 20.

Closure assembly 70 comprises closure member 72 and current collector76. Closure member 72 is molded to contain a vent 82 that will allow theclosure member 72 to rupture if the cell's internal pressure becomesexcessive. Closure member 72 may be made from Nylon 6,6 or anothermaterial, such as a metal, provided the current collector 76 iselectrically insulated from the container 10 which serves as the currentcollector for the first electrode. Current collector 76 is an elongatednail shaped component made of brass. Collector 76 is inserted through acentrally located hole in closure member 72.

The separator is made from nonwoven fibers. One of the separator'sfunctions is to provide a barrier at the interface of the first andsecond electrodes. The barrier must be electrically insulating andionically permeable. A suitable separator is disclosed in WO 03/043103.

The blended zinc powder that is used in a cell of this invention is acombination of at least a first zinc powder and a second zinc powder.The characteristics of the first and second powders must be selected toprovide service and/or cost advantages that are not readily obtainableusing a conventional zinc powder that has been produced in a zinc powderproduction process wherein the full range of zinc particles in the zincpowder's particle size distribution are randomly produced. In such aprocess, the particles have basic physical characteristics that aredetermined by the type of process and the specific conditions used tocontrol the process. The physical characteristics imparted to theparticles by the process have been recognized by the inventor as one ofthe features that can significantly impact how efficiently the zinc willdischarge in an electrochemical cell. For example, the inventor hasrecognized that characteristics of the zinc particles, such as particleroughness and/or particle elongation, in combination with other physicalparameters, such as particle size distribution, can be used to select afirst zinc powder, or a specific particle size distribution within thefirst zinc powder, which can be combined with a second zinc powder, or aspecific particle size distribution within the second zinc powder, tocreate a blended zinc powder that will provide the desired service orcost advantages. As described above, the battery industry that uses zincpowder as an electrochemically active material and the zincmanufacturers that supply the zinc powder have tried to improve thecell's service, also known as the cell's run time, by altering physicalor chemical characteristics of the zinc such as, particle sizedistribution, particle shape and the chemical elements that are alloyedwith the zinc. However, the roughness of the particles, as measured on aroughness index, and the elongation of the particles, as measured on anelongation index, have not been used as criteria to select zinc powdersthat could be mixed together to create a blended zinc powder that wouldprovide service and/or cost advantages.

FIG. 2 is a chart of the roughness of two zinc powders identified hereinas powder A and powder B. Powder A was purchased from N.V. UMICORE,S.A., in Brussels, Belgium and is identified as BIA 115. This zincpowder is an alloy that contains 100 ppm bismuth, 200 ppm indium, and100 ppm aluminum. The powder's D₅₀, which is a measurement used tocharacterize the powder's particle size, was approximately 115. Acentrifugal atomization process, as generally described in WO 00/48260,which published on Aug. 17, 2000, was used to produce the zinc powder.Powder B had the same alloy composition as powder A and was alsopurchased from UMICORE. Powder B was produced in a gas atomizationprocess which is a conventional manufacturing process used to producepowder from a stream of molten zinc. A third process used to manufacturezinc powder is known as impulse atomization and is described in WO2004/012886. The data in FIG. 2 was generated by using screens to sievezinc powders that were produced in either a centrifugal atomizationprocess or a gas atomization process. The powders were sieved asreceived from the manufacturer thereby segregating each of the powdersinto four groups based on particle size range. The ranges were 45 to 75microns, 75 to 105 microns, 105 to 150 microns and greater than 150microns. The roughness of each segregated group was then characterizedusing two dimensional image analysis. The image analysis technique usedan Olympus SZX12 microscope in combination with a digital camera tophotograph zinc particles under sufficient magnification to allow theperimeter of individual particles to be accurately measured. Thetechnique involved evenly distributing a plurality of particles on apiece of glass which was then placed within the viewing field of themicroscope with transmitted light illuminating the particles. Theparticles were arranged to minimize or eliminate particle to particlecontact. The magnification of the microscope was selected to allow atleast ten pixels for small particles. Digital pictures were then takenof different areas of the sample. Each picture had to contain at leasttwo particles that did not touch another particle. Multiple pictureswere taken to obtain 1000 images of particles that did not contactanother particle. Microsuite software, produced by Olympus America Inc.of Melville, N.Y., was used to process the data. The roughness index ofeach group was determined by analyzing images of 1000 particles. Foreach particle, the roughness was determined by dividing the perimeter ofthe particle's image by the perimeter of that particle's equivalentellipse which is defined as an ellipse that has the same area as theparticle and its major axis is equal to the longest dimension of theparticle's image. The roughness index for each group was calculated byaveraging the roughness values of the 1000 particles. A higher roughnessindex means that the particles are rougher than particles with a lowerroughness index. As can be seen in FIG. 2, three of the four groups inpowder A had a higher average roughness index value than thecorresponding groups in powder B. In particular, the particles in powderA that were separated into the 105 to 150 micron range had an averageroughness index value (1.220) that was approximately 3.4 percent higherthan the average roughness index value (1.180) of the correspondinggroup from powder B. Similarly, the particles in powder A that wereseparated into the group consisting of particles greater than 150microns had an average roughness index value (1.245) that wasapproximately 2.9 percent higher than the average roughness index value(1.210) of the corresponding group from powder B. Preferably, theaverage roughness index differential between two powders useful in acell of this invention is at least 2.0 percent, more preferably 3.0percent, even more preferably 3.5 percent.

FIG. 3 is a chart of the elongation index values of the two zinc powderspreviously identified as powder A and powder B. The elongation of 1000particles from each group in powders A and B were characterized usingthe two dimensional image analysis equipment described above. Theelongation index value of each particle was calculated by dividing themajor axis of the equivalent ellipse by the Heywood's diameter of theparticle's image. The Heywood diameter is the diameter of a circle thathas an area that is equivalent to the area of the particle's image. Theaverage elongation index value for each group was determined byaveraging the individual elongation values for the 1000 particles inthat group's sample. The data points in FIG. 3 clearly show that threeof the four groups in powder A consisted of particles that had anaverage elongation index that was at least 4 percent higher than thecorresponding group in powder B. Preferably, an average elongation indexdifferential between two powders useful in cell of this invention is atleast 3.0 percent, more preferably 3.5 percent, even more preferably 4.0percent.

In addition to selecting a first zinc powder and a second zinc powder,or segregated groups of zinc powders, based on their average roughnessindex values and average elongation index values, the particle sizedistribution of the blended zinc powder that is obtained by blending theselected first powder and second powder is known to significantlyinfluence the processability and discharge efficiency of the cellcontaining the blended zinc. Zinc powders that have a particle sizedistribution with a single apex are known herein as unimodal particlesize distribution zinc powders. In FIG. 4, line 80 is an example of aunimodal particle size distribution. If a zinc powder has a particlesize distribution with two or more peaks that define a troughtherebetween, the zinc powder is known herein as a multimodal particlesize distribution zinc powder. In FIG. 4, line 82 is an example of amultimodal particle size distribution. Zinc powders with a unimodalparticle size distribution are often preferred over zinc powders with amultimodal particle size distribution because unimodal powders areeasier to process. Multimodal powders that contain a high percentage ofzinc fines inherently increase the viscosity of the gelled anode thatcontains the multimodal powder. The increase in viscosity can causeprocessing problems in the anode distribution and dispensing equipmentthat is used to transport and dispense the anode.

Preferably, the first and second zinc powders used in a cell of thisinvention are zinc alloys. The alloys contain the same chemicalelements, such as bismuth, indium and aluminum, and the quantities ofthe chemical elements in each alloy are the same.

In one embodiment, a cell of this invention includes a first zinc powderthat has a unimodal particle size distribution but at least one selectedportion of the distribution has been replaced with a similardistribution of zinc particles from a second zinc powder. The particlesfrom the second zinc powder have higher average roughness value than thepowders in the first powder that have been replaced. For example, FIG. 5shows a distribution of zinc powders that has been divided into threeselected portions. The first portion includes particles that flowedthrough a screen that has 75 micron openings. The second portionincludes particles that flowed through a screen that has 150 micronopenings but did not flow through a screen with 75 micron openings. Thethird portion includes particles that would not flow through a screenwith 150 micron openings. Blended zinc powders useful in a cell of thisinvention can be obtained by replacing a selected portion of a zincpowder that has a lower average roughness value with a selected portionof a different zinc powder that has a higher average roughness indexvalue. Preferably, the particle size distribution of the selectedportion of zinc powder does not overlap the particle size distributionof the zinc powder with which it is blended. A first particle sizedistribution is considered not to overlap a second particle sizedistribution if the first distribution is screened or otherwisesegregated using a state of the art commercially available process thatis at least 98% effective, based on the weights of the zinc powdersbefore and after screening, in limiting the powder's particle sizeswithin the desired particle size ranges. While 100% segregation ofpowders is desirable, some processes are not able to prevent smallerzinc particles from clinging to larger particles thereby retaining someof the smaller particles in the distributions of the larger particles.Alternatively, another blended zinc powder useful in a cell of thisinvention could be obtained by replacing a selected portion of a zincpowder that has a higher average roughness index value with a selectedportion of a different zinc powder that has lower average roughnessindex value. Regardless of which powder is segregated into one or moregroups that are then blended with one or more groups from anotherpowder, the net result is a blended zinc powder that has had a selectedportion, based on particle size distribution and surface roughness, ofits zinc particles replaced with particles from another zinc powder'sselected portion.

In another embodiment, a blended zinc powder is produced by blending aselected group from a first powder with a second powder that has notbeen segregated into groups based on surface roughness and particle sizerange. The particles in the first powder's selected group have anaverage roughness index value that is at least two percent higher thanthe average roughness index value of the particles in the second powderfrom the same particle size range which is known herein as the “common”particle size range. For example, if the particles from the firstpowder's selected group have a particle size range between 75 micronsand 105 microns and the second powder has at least some of its particlesin the 75 to 105 micron range, then the first and second powder haveparticles in a common particle size range. This embodiment provides forthe blending of a selected “common” group from a first powder with asecond powder having particles in the same “common” particle size rangeas the first powder's provided the particles from the first powder arerougher than the particles in the second powder's common particle sizerange.

In another embodiment, a blended zinc powder useful in a cell of thisinvention can be obtained by mixing two zinc powders that haveessentially the same particle size distributions but the averageroughness and/or elongation index values of the first powder's selectedportion is higher than the average roughness and/or elongation indexvalues of the same selected portion in the second zinc powder. In thisembodiment, the particle size distribution of the blended zinc powder isthe same as the particle size distributions of the two powders that areblended but the blended powder contains particles that are rougherand/or more elongated that the particles in one of the powders.

Blending zinc powders that have different roughness and/or elongationindex values provides cell manufacturers with the ability to tailor thecost-to-performance characteristics of the blended zinc powder. Forexample, if a first zinc powder is know to provide superior service inan electrochemical cell but the powder is more expensive than anotherzinc powder which provides less run time, the cell manufacturer canelect to remove a selected portion of the less expensive powder andreplace it with a portion of the more expensive powder. The result is ablended powder that is less expensive than the more expensive powderand, as shown in FIG. 6, the service performance of the cells containingthe blended zinc may be equal to or better than the service performanceof the cells that contain only the more expensive zinc. The ability totailor the cost-to-performance ratio of the blended powder provides thecell designer with an option that is not available with unblended zincpowders.

A process that can be used to produce blended zinc powders for use in acell of this invention includes the following steps. Segregating a firstpowder into at least two groups based on particle size. Segregating asecond powder into at least two groups based on particle size. Whereinat least one group from the first powder and one group from the secondpowder have a common particle size range and the particles in the firstpowder's common particle size range have an average roughness indexvalue that is at least 2.0 percent higher than the average roughnessindex value of the particles in the second powder's common particle sizerange. Then blending at least one group from the first powder with atleast one group from the second group thereby forming a blended zincpowder.

The term “blended” when used in the phrase “blended zinc powder” isintended to describe two or more zinc powders that have been mixed,tumbled, stirred or otherwise physically agitated to provide ahomogenous distribution of zinc particles from the two or more zincpowders.

To illustrate the service advantages that can be obtained by usingblended zinc powders of the present invention, eight lots of AA sizebatteries, having a cell construction similar to that shown in FIG. 1and described above, were manufactured and discharged on three high ratedischarge tests. The cathodes, separators, electrolyte, seal assembliesand anode formulas, other than the zinc powder, used in each cell wereidentical. The zinc powders used in each lot were obtained as follows. Afirst zinc powder, designated earlier as powder A, was obtained fromUMICORE. This powder was an alloy of zinc containing 100 ppm bismuth,200 ppm indium and 100 ppm aluminum, as previously described. The powderwas produced in a centrifugal atomization process and had a D₅₀ of 115microns. Powder A was screened to produce a first group, designated A-1,with particles that passed through a screen with 75 micron openings, asecond group, designated A-2, with particles that did flow through ascreen with 150 micron openings but would not flow through a screen with75 micron openings, and a third group, designated A-3, with particlesthat would not flow through a screen with 150 micron openings. A secondpowder, designated earlier as powder B, was also obtained from UMICORE.This powder, which was an alloy of zinc containing 100 ppm of bismuth,200 ppm of indium and 100 ppm of aluminum, was produced in a centrifugalatomization process and had a D₅₀ of 160 microns. Powder B was alsoscreened to produce a first group, designated B-1, with particles thatpassed through a screen with 75 micron openings, a second group,designated B-2, with particles that did flow through a screen with 150micron openings but would not flow through a screen with 75 micronopenings, and a third group, designated B-3, with particles that wouldnot flow through a screen with 150 micron openings. Eight differentblended zinc powders, designated lots 100 to 107 in FIG. 6, wereobtained by blending various combinations of the groups from the twozinc powders. Lot 100 contained only zinc powder from powder B. Lot 101contained groups A-1, B-2 and B-3. In this blend, the particle sizerange of the particles from powder A was less than the particle sizerange of the particles from powder B. Lot 102 contained groups B-1, A-2and B-3. Lot 103 contained groups B-1, B-2 and A-3. Lot 104 containedgroups B-1, A-2 and A-3. Lot 105 contained groups A-1, B-2 and A-3. Lot106 contained groups A-1, A-2 and B-3. Lot 107 contained groups A-1, A-2and A-3. The data in FIG. 6 was obtained by discharging five batteriesfrom each lot in each of the following three discharge tests which wereall done in a 21° C. environment. In the first discharge test, each cellwas discharged continuously at one amp until the cell's closed circuitvoltage dropped below 1.0 volt. In the second discharge test, each cellwas discharged repeatedly at one watt for three seconds and then allowedto rest for seven seconds. This discharge regime was repeatedcontinuously until the cell's closed circuit voltage dropped below 0.9volt. In the third discharge test, each cell was discharged continuouslyat one watt until the cell's closed circuit voltage dropped below 1.0volt. The amount of time each cell remained on test and above thevoltage cutoff was recorded and then averaged to obtain an average runtime for each lot on each test. The average discharge times of the cellsin lot 100 were selected as the standard against which all other celldischarge times were normalized. The data in FIG. 6 clearly shows thatthe cells that contained blended zinc powder (lots 101 through 106,inclusive) provided substantially higher service than the cells thatcontained only powder B (lot 100) and, furthermore, the cells thatcontained the blended zinc powder provided more minutes of run time thanthe cells that contained only powder A on both the one amp continuoustest and the one watt continuous test. Clearly, the range of run timesin lots 101 through 106 demonstrate that the mixing of groups of zincpowders, segregated by particle size distributions, provides cellmanufacturers with the ability to choose the desired level of run timeby selecting which groups to combine into a blended zinc powder.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and are not intended to limitthe scope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including theDoctrine of Equivalents.

1. An electrochemical cell, comprising: a first electrode including ablended zinc powder comprising at least a first zinc powder and a secondzinc powder, said first and second powders have particles within acommon particle size range, wherein the first powder's particles in saidcommon particle size range have a average roughness index value that isat least 2.0 percent higher than the average roughness index value ofthe second powder's particles in said common particle size range.
 2. Theelectrochemical cell of claim 1 wherein the average roughness indexvalue of the first powder's particles in said common particle size rangeis at least 3.0 percent higher than the average roughness index value ofthe second powder's particles in said common particle size range.
 3. Theelectrochemical cell of claim 2 wherein the average roughness indexvalue of the first powder's particles in said common particle size rangeis at least 3.5 percent higher than the average roughness index value ofthe second powder's particles in said common particle size range.
 4. Theelectrochemical cell of claim 1 wherein the average elongation indexvalue of the first powder's particles in said common particle size rangeis at least 3 percent greater than the average elongation value of thesecond powder's particles in said common particle size range.
 5. Theelectrochemical cell of claim 4 wherein the average elongation indexvalue of the first powder's particles in said common particle size rangeis at least 3.5 percent greater than the average elongation value of thesecond powder's particles in said common particle size range.
 6. Theelectrochemical cell of claim 5 wherein the average elongation indexvalue of the first powder's particles in said common particle size rangeis at least 4.0 percent greater than the average elongation value of thesecond powder's particles in said common particle size range.
 7. Theelectrochemical cell of claim 1, wherein said first powder is formed ina first powder manufacturing process, said second powder is formed in asecond powder manufacturing process and said first and second powdermanufacturing processes are different from one another.
 8. Theelectrochemical cell of claim 7, wherein said powder manufacturingprocesses are selected from the group consisting of centrifugalatomization, gas atomization, and impulse atomization.
 9. Theelectrochemical cell of claim 1 further including a container, saidcontainer housing said first electrode comprising said blended zincpowder, a second electrode comprising manganese dioxide, a separatorlocated between said electrodes, and an alkaline electrolyte in contactwith the separator and both electrodes.
 10. The electrochemical cell ofclaim 1 wherein said first powder and said second powder are zinc alloyscomprising the same chemical elements.
 11. The electrochemical cell ofclaim 10 wherein the quantities of said chemical elements in said alloysare the same.
 12. An electrochemical cell comprising a first electrodeincluding a mixture of zinc powders, said mixture comprising zincparticles from a first powder and zinc particles from at least a secondpowder, wherein the range of particle sizes in the first powder and therange of particle sizes in the second powder do not overlap.
 13. Theelectrochemical cell of claim 12 wherein said first powder's particleshave a particle size less than 75 microns and said second powder'sparticles have a particle size greater than 75 microns.
 14. Theelectrochemical cell of claim 12 wherein said first powder's particleshave a particle size between 75 microns and 150 microns and said secondpowder's particles comprise a first group having a particle size greaterthan 150 microns and a second group having a particle size less lessthan 75 microns.
 15. The electrochemical cell of claim 12 wherein saidfirst powder's particles have a particle size greater than 150 micronsand said second powder's particles have a particle size less than 150microns.
 16. The electrochemical cell of claim 12 wherein said mixtureof zinc powders has a unimodal particle size distribution.
 17. Anelectrochemical cell comprising a first electrode including a mixture ofzinc powders obtained by segregating a first powder into at least twogroups based on particle size, segregating a second powder into at leasttwo groups based on particle size wherein at least one group from thefirst powder and at least one group from the second powder have a commonparticle size range and the group in the first powder's common particlesize range has an average roughness index value that is at least 2.0percent higher than the average roughness index value of the group inthe second powder's common particle size range, and then blending thegroup from the first powder's common particle size range with at leastone group from the second powder.
 18. The electrochemical cell of claim17 wherein said second powder's group has a particle size range thatdoes not include said common particle size range.
 19. Theelectrochemical cell of claim 17 wherein said first powder's group has aparticle size range less than 75 microns and said second powder's grouphas a particle size range greater than 75 microns.
 20. Theelectrochemical cell of claim 17 wherein said first powder's group has aparticle size range between 75 microns and 150 microns and said secondpowder's group comprises a first portion having a particle size rangegreater than 150 microns and a second portion having a particle sizerange less than 75 microns.
 21. The electrochemical cell of claim 17wherein said first powder's group has a particle size range greater than150 microns and said second powder's group has a particle size rangeless than 150 microns.
 22. The electrochemical cell of claim 17 whereinthe average roughness index value of the first powder's group in saidcommon particle size range is at least 3.0 percent higher than theaverage roughness index value of the second powder's group in saidcommon particle size range.
 23. The electrochemical cell of claim 22wherein the average roughness index value of the first powder's group insaid common particle size range is at least 3.5 percent higher than theaverage roughness index value of the second powder's group in saidcommon particle size range.
 24. The electrochemical cell of claim 17wherein the average elongation index value of the first powder's groupin said common particle size range is at least 3.0 percent greater thanthe average elongation value of the second powder's group in said commonparticle size range.
 25. The electrochemical cell of claim 24 whereinthe average elongation index value of the first powder's group in saidcommon particle size range is at least 3.5 percent greater than theaverage elongation value of the second powder's group in said commonparticle size range.
 26. The electrochemical cell of claim 25 whereinthe average elongation index value of the first powder's group in saidcommon particle size range is at least 4.0 percent greater than theaverage elongation value of the second powder's group in said commonparticle size range.
 27. The electrochemical cell of claim 17, whereinsaid first powder is formed in a first powder manufacturing process,said second powder is produced in a second powder manufacturing processand said first and second powder manufacturing processes are differentfrom one another.
 28. The electrochemical cell of claim 27, wherein saidpowder manufacturing processes are selected from the group consisting ofcentrifugal atomization, gas atomization, and impulse atomization. 29.The electrochemical cell of claim 17 further including a container, saidcontainer housing said first electrode comprising said mixture of zincpowder, a second electrode comprising manganese dioxide, a separatorlocated between said electrodes, and an alkaline electrolyte in contactwith the separator and both electrodes.
 30. The electrochemical cell ofclaim 17 wherein said first powder and said second powder are zincalloys comprising the same chemical elements.
 31. The electrochemicalcell of claim 30 wherein the quantities of said chemical elements insaid alloys are the same.
 32. A process for producing a blended zincpowder comprising the steps of: segregating a first powder into at leasttwo groups based on particle size; segregating a second powder into atleast two groups based on particle size; and blending at least one groupfrom the first powder with at least one group from the second powderthereby forming said blended zinc powder, wherein at least one groupfrom the first powder and one group from the second powder have a commonparticle size range and the particles in the first powder's commonparticle size range have an average roughness index value that is atleast 2.0 percent higher than the average roughness index value of theparticles in the second powder's common particle size range.
 33. Theprocess of claim 32 wherein said at least one group from said secondpowder has a particle size range that does not include said commonparticle size range.
 34. The process of claim 32 wherein the averageroughness index value of the first powder's particles in said commonparticle size range is at least 3.0 percent higher than the averageroughness index value of the second powder's particles in said commonparticle size range.
 35. The process of claim 34 wherein the averageroughness index value of the first powder's particles in said commonparticle size range is at least 3.5 percent higher than the averageroughness index value of the second powder's particles in said commonparticle size range.
 36. The process of claim 32 wherein the averageelongation index value of the first powder's particles in said commonparticle size range is at least 3.0 percent greater than the averageelongation value of the second powder's particles in said commonparticle size range.
 37. The process of claim 36 wherein the averageelongation index value of the first powder's particles in said commonparticle size range is at least 3.5 percent greater than the averageelongation value of the second powder's particles in said commonparticle size range.
 38. The process of claim 37 wherein the averageelongation index value of the first powder's particles in said commonparticle size range is at least 4.0 percent greater than the averageelongation value of the second powder's particles in said commonparticle size range.
 39. The process of claim 32, wherein said firstpowder is formed in a first powder manufacturing process, said secondpowder is produced in a second powder manufacturing process and saidfirst and second powder manufacturing processes are different from oneanother.
 40. The process of claim 32, wherein said powder manufacturingprocesses are selected from the group consisting of centrifugalatomization, gas atomization, and impulse atomization.
 41. The processof claim 32 wherein said first powder and said second powder are zincalloys comprising the same chemical elements.
 42. The process of claim41 wherein the quantities of said chemical elements in said alloys arethe same.
 43. The process of claim 32 wherein said blended zinc powderhas a unimodal particle size distribution.